Question: Given that 10 is the arithmetic mean of the set $\{6, 13, 18, 4, x\}$, what is the value of $x$?
Explanation: There are 5 numbers in this set, so we have \begin{align*} \frac{6+13+18+4+x}{5}&=10 \\ 6+13+18+4+x&=50 \\ 6+4+13+18+x&=50 \\ 10+31+x &=50 \\ 41+x&=50 \\ x &= \boxed{9} \end{align*}